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// Copyright 2020 Parity Technologies
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::marker::PhantomData;
use std::ops::Deref;

use digest::generic_array::{
	typenum::{U20, U32, U64},
	GenericArray,
};
use sha2::Digest as RDigest;

/// The message digest.
pub struct Digest<T>(InnerDigest, PhantomData<T>);

enum InnerDigest {
	Sha256(GenericArray<u8, U32>),
	Sha512(GenericArray<u8, U64>),
	Ripemd160(GenericArray<u8, U20>),
}

impl<T> Deref for Digest<T> {
	type Target = [u8];
	fn deref(&self) -> &Self::Target {
		match self.0 {
			InnerDigest::Sha256(ref d) => &d[..],
			InnerDigest::Sha512(ref d) => &d[..],
			InnerDigest::Ripemd160(ref d) => &d[..],
		}
	}
}

/// Single-step sha256 digest computation.
pub fn sha256(data: &[u8]) -> Digest<Sha256> {
	let mut hasher = Hasher::sha256();
	hasher.update(data);
	hasher.finish()
}

/// Single-step sha512 digest computation.
pub fn sha512(data: &[u8]) -> Digest<Sha512> {
	let mut hasher = Hasher::sha512();
	hasher.update(data);
	hasher.finish()
}

/// Single-step ripemd160 digest computation.
pub fn ripemd160(data: &[u8]) -> Digest<Ripemd160> {
	let mut hasher = Hasher::ripemd160();
	hasher.update(data);
	hasher.finish()
}

#[derive(Debug)]
pub enum Sha256 {}
#[derive(Debug)]
pub enum Sha512 {}
#[derive(Debug)]
pub enum Ripemd160 {}

/// Stateful digest computation.
pub struct Hasher<T>(Inner, PhantomData<T>);

enum Inner {
	Sha256(sha2::Sha256),
	Sha512(sha2::Sha512),
	Ripemd160(ripemd160::Ripemd160),
}

impl Hasher<Sha256> {
	pub fn sha256() -> Hasher<Sha256> {
		Hasher(Inner::Sha256(sha2::Sha256::default()), PhantomData)
	}
}

impl Hasher<Sha512> {
	pub fn sha512() -> Hasher<Sha512> {
		Hasher(Inner::Sha512(sha2::Sha512::default()), PhantomData)
	}
}

impl Hasher<Ripemd160> {
	pub fn ripemd160() -> Hasher<Ripemd160> {
		Hasher(Inner::Ripemd160(ripemd160::Ripemd160::default()), PhantomData)
	}
}

impl<T> Hasher<T> {
	pub fn update(&mut self, data: &[u8]) {
		match self.0 {
			Inner::Sha256(ref mut ctx) => ctx.update(data),
			Inner::Sha512(ref mut ctx) => ctx.update(data),
			Inner::Ripemd160(ref mut ctx) => ctx.update(data),
		}
	}

	pub fn finish(self) -> Digest<T> {
		match self.0 {
			Inner::Sha256(ctx) => Digest(InnerDigest::Sha256(ctx.finalize()), PhantomData),
			Inner::Sha512(ctx) => Digest(InnerDigest::Sha512(ctx.finalize()), PhantomData),
			Inner::Ripemd160(ctx) => Digest(InnerDigest::Ripemd160(ctx.finalize()), PhantomData),
		}
	}
}